Recently, as a substrate gets larger, it is requested that a plasma processing apparatus get larger. In order to uniformly perform plasma processing on a substrate having a large area, it is preferable that a plurality of power supply points of electromagnetic waves are used. For example, in order to uniformly supply power in a large apparatus, a method of uniformly supplying electromagnetic waves to an entire ceiling surface of an apparatus by arranging a plurality of coaxial waveguides as power supply points in an array on the ceiling surface of the apparatus and supplying electromagnetic waves having the same amplitude and the same phase from the plurality of coaxial waveguides is suggested (see, for example, Patent Document 1). Accordingly, gas ionization or gas dissociation is accelerated uniformly on the entire ceiling surface, and thus plasma can be uniformly formed under the ceiling surface even if the apparatus is large and a good plasma process can be performed on the substrate by using the generated plasma.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2008-305736